Dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) are circulating secretory products of the adrenal cortex that decline profoundly with age. The underlying rationale for this project is that the age-related decline of DHEA and DHEAS may be causally related to an increased risk of developing cancer and atherosclerosis, and that protection against such risks may be achieved by restoring the levels of these steroids to those prevailing in youth. DHEA is protective in many experimental carcinogenesis models. DHEA is also an uncompetitive inhibitor of isolated mammalian glucose-6-phosphate dehydrogenases (G6PD). We have established that DHEA and related steroidal inhibitors of G6PD block the differentiation of 3T3-L1 fibroblasts to adipocytes. Therefore, biochemical and molecular techniques will be used to raise intracellular G6PD levels, and the effects of this maneuver on the steroid block will be examined. The potential metabolic importance of the highly unusual uncompetitive inhibition of G6PD by DHEA and related steroids is to be clarified through detailed analysis of the effects of DHEA (and DHEA conjugates) on the binding of substrates to purified human G6PD, by use of kinetic and fluorescence (protein and nicotinamide nucleotide) techniques. In a population-based approach, the risk of low levels of DHEA and DHEAS for the development of specific malignancies will be examined in carefully selected and control-matched human sera collected 15 years ago from almost 26,000 individuals whose health histories have been carefully monitored. Over 1,800 individuals have now developed cancer. It is also planned to develop reliable short-term markers for the chemoprotective activity of DHEA by monitoring levels of 6-phosphogluconate and other pentose phosphate pathway intermediates in easily-accessible tissue compartments. these combined laboratory and population-based studies should provide a better understanding of the protective role of DHEA against cancer and atherosclerosis, and the prospects of its use as a chemoprotective agent.